Referring to FIGS. 1 to 4, there is shown a microswitch of the type described herein as disclosed in the prior Japanese Utility Model Application Kokai No. 1-132025 commonly assigned to the assignee of the present invention.
As seen in FIG. 1 which is an exploded view, this microswitch comprises a generally rectangular body 20 formed of an electrically insulating material, actuators 10, coil springs 26 for biasing the respective actuators !0 outwardly, a cover 30 of an electrically insulating material closing the top of the body 20, and movable contact members in the form of contact springs 19 associated with the respective actuators.
The body 20 is formed with a pair of juxtaposed open topped switch compartments 20R for accommodating the associated actuators to constitute two switch circuits, only one of which is shown in the drawings. As illustrated in FIG. 2 which is a cross-sectional view taken along line II--II in FIG. 1, first and second fixed contact members 23C and 24C are secured to the opposed inner walls of each of the switch compartments 2OR.
The cover 30 has a pair of through-bores 32 extending therethrough in facing relation with the respective compartments 20R and a pair of vertically extending tubular guide portions 33 integrally formed therewith in concentric alignment with and communicating with the respective through-bores 32.
The cover 30 further has a pair of U-shaped catch lugs 31 depending from its opposite side edges which are engageable with corresponding detent pawls 28 protruding from the opposed side walls of the body 20 to thereby lock the cover to the body. As seen in FIGS. 1 and 2, first and second terminals 23 and 24 integral with the first and second fixed contact members 23C and 24C, respectively extend out from one outer side wall of the body 20.
Each of the actuators 10 comprises a flat generally box-shaped contact holder block 12 and an integral vertical stem portion 13 upstanding from the top surface of the holder block and adapted to be accommodated in the associated compartment 20R with the coil spring 26 disposed between the undersurface of the holder block and the bottom wall of the compartment. The stem portion 13 is telescopically inserted through the through-bore 32 in the cover 30 and the tubular guide portion 33.
The contact spring 19 is made of a single piece of resilient wire bent so as to form a central coiled portion 19B and a pair of arms 19A extending from the opposite ends of the coiled portion with an angle of about 70.degree. therebetween, the arms 19A being inwardly bent toward each other at about 90.degree. adjacent their outer free ends to form first and second convex contact portions 19C1 and 19C2.
The contact spring 19 is held in a flat housing slot 11 in the holder block 12 of the actuator 10, the housing slot 11 extending in the holder block from one end face (front end face) 12A toward the opposed end face (rear end face) 12B of the block parallel to the top surface of the block and dissecting the front end face 12A.
The holder block 12 is formed with slits 14 through the opposed side walls 12C, 12D perpendicular to the front end face 12A, the slits 14 communicating with the housing slot 11 so that the first and second convex contact portions 19C1, 19C2 of the contact spring 19 may protrude out through the slits. Extending generally perpendicularly from the front end face 12A and rear end face 12B are guide projections 15 and 16, respectively which are adapted to be received in and guided along guide grooves 21, 22, respectively formed in the opposed walls of the switch compartment 20R as the actuator 10 is moved upwardly and downwardly in the compartment 2OR.
The vertical movements of the actuator 10 will resiliently bring the first and second contact portions 19C1, 19C2 of the contact spring 19 into and out of slidable contact with the first and second fixed contact members 23C and 24C, respectively. The bottom wall of the compartment 20R is formed with a circular recess 25 to seat in place the coil spring 26, the top end of which is engaged with a boss 17 formed on the bottom surface of the holder block 12 to resiliently urge the actuator 10 outwardly or upwardly.
In the state as shown in FIG. 4A in which the actuator 10 is raised into abutment against the cover 30 by the coil spring 26, the first and second contact portions 19C1, 19C2 are in engagement with the walls of the compartment 2OR, but out of contact with the first and second fixed contact members 23C, 24C, whereby the first and second fixed contact members 23C, 24C are electrically out of contact with each other to turn the switch off.
Upon depressing the actuator 10 down into the compartment against the biasing force of the spring 26, the first and second contact portions 19C1, 19C2 are brought into resilient and slidable contact with the first and second fixed contact members 23C, 24C, whereby the first and second fixed contact members 23C and 24C are electrically connected with each other through the movable contact member 19 to turn the switch on.
Upon the applied force on the actuator 10 being released, the coil spring 26 will again raise the actuator 10 out of engagement with the first and second fixed contact members 23C, 24C to turn the switch off.
With the switch constructed as described above, the first and second contact portions 19C1, 19C2 are moved in slidable contact with the first and second fixed contact members 23C, 24C, and the contact surfaces are cleaned at all times. In addition, a light actuating motion will ensure a good electrical contact, thereby enhancing the reliability of the switch. Another advantage is that the movable contact member 19 may be reduced in thickness and the axial length of the coil spring 26 may also be reduced as compared to the prior art, making it possible to further reduce the size of the switch.
However, as the switch is made more compact, the components thereof are naturally correspondingly reduced in size. By way of illustration, the wire of which the contact spring 19 is formed is typically 0.16 mm in diameter. The length of each of arms 19A is as short as 2 mm and the diameter of the coiled portion 19B is only about 1 mm. Accordingly, in placing (assembling) the movable contact member 19 into the contact holder block 12 of the actuator 10, the use of a pincette to grasp and push the movable contact member into the holder block in a conventional manner would badly reduce the working efficiency as well as possibly deforming the movable contact member as it is inserted, resulting in lowering reliability.